Subj: fyi.... article on quakes in Trinidad, CO
Date: 9/7/01 5:36:39 AM Pacific Daylight Time

Click here: Rocky Mountain News: State,1299,DRMN_21_818841,00.html

Trinidad quakes investigated:   8 small temblors have occurred near the city in the past two weeks

By Jim Erickson, News Science Writer
Rocky Mountain News ~ Denver, Colorado
September 7, 2001

The U.S. Geological Survey sent a team to the Trinidad area Thursday to investigate a "swarm" of eight small earthquakes that have jolted the border area over the past two weeks.

Two more small earthquakes were recorded early Thursday. A magnitude 3.6 quake was detected at 3:42 a.m., and a magnitude 3.5 quake occurred at 5:28 a.m. A quake of magnitude 2.5 to 3 is the smallest generally felt by people.

Seven portable digital seismographs will be installed west of Trinidad to record ground motion and to help pinpoint the fault that's causing the tremors, said Anthony Crone, assistant chief scientist for the federal agency's geologic hazards team in Golden.

The quakes are occurring in an area with no known faults, Crone said.

"The part that is unusual about this is that we haven't had similar sort of activity, at least in the historical record, in this part of the state," Crone said Thursday. "We don't have any evidence of a similar number of events in such a short period of time.

"That creates scientific curiosity about what has initiated this swarm and what it means in terms of the geological conditions in the area," he said. "But we have no basis, at this point, for even having any inkling that this is a precursor to something more serious."

The largest of the eight quakes since Aug. 28 was a magnitude 4.5 on Wednesday. All the tremors occurred five to 15 miles west southwest of Trinidad, said Waverly Person, chief of the geological survey's Earthquake Information Center.

The tremors were detected by geological survey instruments in Albuquerque and Idaho Springs. Because those seismic stations are so far from Trinidad, researchers suspect they may be missing many smaller quakes near the town.

The portable seismographs will allow researchers to detect very small earthquakes, which will help them zero in on the fault or faults that are generating them. A fault is a crack in the Earth, and an earthquake occurs when there is movement along that fissure.

"If you have six, seven or eight magnitude 3's, you may also be having several dozen or more magnitude 2 events, and maybe tens or hundreds of magnitude 1 events," Crone said.

Human activities sometimes can trigger earthquakes and swarms of quakes. In 1968, fluids were injected 11,000 feet into the ground at the Rocky Mountain Arsenal, triggering hundreds of small earthquakes, Crone said.

Coal was mined around Trinidad in the past, and there are natural gas wells in the area today. There is no indication that human activity triggered the current series of tremors, but researchers "will take a look at what other explanations there are for the swarm," Crone said.

A major earthquake has never been reported in Colorado. The biggest quake reported in the state was a magnitude 6.6 in 1882 just west of Fort Collins. It caused damage as far away as Denver.

In 1967, a magnitude 5.3 quake shook Thornton, Northglenn and Commerce City, causing about $1 million in damage and a few injuries, Person said.

"As far as we know from history, no one has ever been killed from an earthquake in the state of Colorado," he said.